N-(hetero)arylazoles are compounds useful as medical or agrochemical products, organic photoconductors, organic electroluminescent element materials, and the like. These compounds have conventionally been produced by the Ullmann reaction, known as a process for synthesizing N-(hetero)arylamines, wherein a copper compound is used as a catalyst. The original Ullmann reaction involves such defects as use of a large amount of catalyst, harsh reaction conditions, limitation as to substrates, and complicated after-treatment, and has long been believed to be a reaction having poor usefulness. With the development of research in recent years, significant improvements are being made. However, there still remains the defect that a substrate which is highly reactive but is expensive, such as (hetero)aryl bromide, (hetero)aryl iodide, or (hetero)aryl boronic acid, is required.
With such background, an arylamination using a palladium compound as a catalyst (Buchwald-Hartwig amination) was developed in the 1990s. In comparison with the Ullmann reaction, this reaction uses a smaller amount of catalyst, reaction conditions for the reaction are milder, substrate generality is more extensive and, in addition, experimental procedures are comparatively easy. Further, even (hetero)aryl chlorides, which are inexpensive and readily available but which have been believed to be difficult to use due to their poor reactivity, becomes employable as the substrate by using an appropriate (i.e., electron-rich and bulky) coordination compound. Therefore, the reaction has attracted attention as a novel process for synthesizing N-(hetero)arylamines. Even now, fundamental investigations on the process are being made actively and, in addition, this reaction has come into wide use in the industrial production of chemical products (for example, Non-Patent Literature 1).
However, only a few reports have been made on application of the Buchwald-Hartwig amination to synthesis of N-(hetero)arylazoles (for example, Non-Patent Literature 2 to 7). Use of a base is necessary for this reaction, and alkali metal compounds are used in common as a base in these reports. Some of these reactions proceed under comparatively moderate conditions and permit use of (hetero)aryl chlorides (Non-Patent Literature 3, 4, 5, and 7). Additionally, regarding the Buchwald-Hartwig amination, the concept itself of using not an alkali metal compound but a magnesium compound as the base has long been proposed (Patent Literature 1).
On the other hand, there has been reported in recent years a reaction between indole which is one kind of NH-azoles and an aryl halide in which various magnesium compounds are used as bases in the presence of the catalyst composed of palladium(II) acetate and triphenylphosphine (Non-Patent Literature 8).
It has been reported very recently that, only when carbazole which is one kind of NH-azoles is used as a substrate, even by using a magnesium compound as a base, an intended N-arylcarbazole can be obtained in the presence of the catalyst composed of dichlorobis(triphenylphosphine)nickel(II) and triphenylphospnine (Non-Patent Literature 9).